This invention relates to nonlinear and bistable optical devices and, more particularly, to nonlinear and bistable optical devices that utilize a Kerr medium, that is, a medium in which the index of refraction is a function of the optical intensity within the medium.
The prior art has produced a nonlinear device that utilizes a Kerr medium. See the article entitled "Theory of Nonresonant Multistable Optical Devices," F. S. Felber and J. H. Marburger, Applied Physics Letters, Vol. 28, No. 12, June 15, 1976, pp. 731-733. In this Felber et al device, the Kerr medium substantially fills an interferometer cavity. This type of device was suggested by Felber et al in order to provide a bistable interferometer which is not dependent on the resonant or absorption parameters of the medium as in still other prior art interferometer devices. As taught by Felber et al, this type of interferometer device with a Kerr medium in theory at least provides a bistable device which exhibits differential gain and may be utilized as a memory element, a power limiter or optical switch providing the device is suitably biased. Since the effect utilized does not depend on any resonant properties of the medium, the device may be biased by an independent field whose frequency differs from that of the field being amplified. Since the dependence of the refractive index on light intensity is a very weak effect for all known materials, devices such as the Felber et al device require high light intensities. The Felber et al device requires power densities in the order of 10.sup.8 watts/cm.sup.2. The use of a Fabry-Perot interferometer not only restricts the response time of the device to be at least as long as the build-up time of the interferometer, but also requires that the input radiation be restricted to a narrow bandwidth.
In still another prior art device, nonlinear and bistable characteristics are provided by an interferometer cavity that is substantially filled with an electro-optic material having terminals to which a potential can be applied. Since the index of refraction of this electro-optic material is dependent on this potential, the cavity can be tuned by changing the magnitude of the potential applied to the electro-optic medium. A photodetector is caused to be responsive to the energy density of the optical radiation within the cavity and the potential developed by this photodetector is coupled to the terminals of the electro-optic medium. The resulting device exhibits external characteristics that are similar to those predicted for the Felber et al device, but it does so when using optical radiation that can be many orders of magnitude lower in power than that required when using a Kerr medium in an interferometer device. Restrictions caused by the use of a Fabry-Perot interferometer are the same as those for the Felber et al device. In addition, the response time may be further limited by the electrical circuitry. Devices which use an electro-optic medium within an interferometer cavity are disclosed in patent application Ser. No. 902,733, filed on May 3, 1978, by P. W. Smith, and in the article entitled "A Bistable Fabry Perot Resonator," by P. W. Smith and E. H. Turner, Applied Physics Letters, Vol. 30, No. 6, Mar. 15, 1977, pp. 280-281.